Computerized visualization systems are used in many fields such as computer gaming, three-dimensional modeling, and advanced scientific visualization, for example digital microscopy. Typically, computerized visualization systems use camera models with central or parallel projection for obtaining images from input data defining three-dimensional scenes. Images are obtained by projecting three-dimensional objects onto a view (projection) plane (or view port) and then mapping the view plane onto a two-dimensional display. In a camera model with central projection, projection lines emanate from the center of projection, the defined viewpoint. Images are obtained by parallel projection with camera models having the viewpoint set at an infinite distance from the view projection plane. The intersection of the projection lines with the view projection plane forms the projected two-dimensional image of the three-dimensional object. Thus a three-dimensional scene is shown on the two-dimensional display as projected onto the camera model's view projection plane from the camera model's defined viewpoint. The representation of the three-dimensional scene on the two-dimensional display lacks indication of depth and distance. Particularly, in three-dimensional scenes comprising numerous objects of unknown shape or size, a user is left without any visual cues for depth perception. Consequently, it is very difficult for a user to place a pointer, i.e. a cursor, in a three-dimensional scene. Hereafter, the camera model of a computerized visualization system, defined by its view projection plane and viewpoint, is also referred to as “camera”.
In U.S. Pat. No. 6,057,827 a computer graphics modeling system is described which makes it possible for a user to position a cursor accurately on a geometric point of a three-dimensional object. According to U.S. Pat. No. 6,057,827, in response to a user signal, the cursor is moved automatically to the geometric point of the three-dimensional object nearest to the present position of the cursor. Nevertheless, without any additional visual cues, the user is still required to move the cursor to a close proximity of the three-dimensional object while the user receives no visual cues for the depth positioning of the cursor.
An improved depth perception can be achieved by adding means for stereoscopic vision to the visualization system. However, not all users are able to obtain an improved depth perception from stereoscopic vision. Moreover, hardware devices, such as binoculars or filtering glasses, required for obtaining the stereoscopic vision, are often found impractical or inconvenient by the users.